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loro-websocket

WebSocket client and a minimal SimpleServer for syncing Loro CRDTs. The client provides connection status events, auto‑reconnect with exponential backoff, latency tracking via ping/pong, safe fragmentation/reassembly for large updates, and seamless room rejoin across reconnects.

Install

pnpm add loro-websocket loro-adaptors loro-protocol
# plus peer dep in your app
pnpm add loro-crdt

Quick Start

// In Node, provide a WebSocket implementation
import { WebSocket } from "ws";
(globalThis as any).WebSocket =
  WebSocket as unknown as typeof globalThis.WebSocket;

import { LoroWebsocketClient, ClientStatus } from "loro-websocket";
import { LoroAdaptor } from "loro-adaptors/loro";

const client = new LoroWebsocketClient({ url: "ws://localhost:8787" });

// React to connection status
const offStatus = client.onStatusChange(s => console.log("status:", s));

await client.waitConnected();

// Join a room with a CRDT adaptor
const adaptor = new LoroAdaptor();
const room = await client.join({ roomId: "demo", crdtAdaptor: adaptor });

// Edit document and sync
const text = adaptor.getDoc().getText("content");
text.insert(0, "Hello, Loro!");
adaptor.getDoc().commit();

await room.destroy();
offStatus();

%ELO (end‑to‑end encrypted Loro) using EloAdaptor:

import { LoroWebsocketClient } from "loro-websocket";
import { EloAdaptor } from "loro-adaptors/loro";

const key = new Uint8Array(32);
key[0] = 1;
const client = new LoroWebsocketClient({ url: "ws://localhost:8787" });
await client.waitConnected();

const adaptor = new EloAdaptor({
  getPrivateKey: async () => ({ keyId: "k1", key }),
});
await client.join({ roomId: "secure-room", crdtAdaptor: adaptor });

adaptor.getDoc().getText("t").insert(0, "secret");
adaptor.getDoc().commit();

Client API

new LoroWebsocketClient(options: LoroWebsocketClientOptions)

interface LoroWebsocketClientOptions {
  url: string;                 // WebSocket URL (ws:// or wss://)
  pingIntervalMs?: number;     // Periodic ping interval (default 20_000ms)
  disablePing?: boolean;       // Disable periodic pings entirely
  onWsClose?: () => void;      // Low‑level ws close callback (before status transitions)
}

// Status values (no enums)
const ClientStatus = {
  Connecting: "connecting",
  Connected: "connected",
  Disconnected: "disconnected",
} as const;
type ClientStatusValue = typeof ClientStatus[keyof typeof ClientStatus];

  • Connection

    • waitConnected(): Promise<void> resolves once the socket is open.
    • connect(): Promise<void> manually initiate/resume connection; also re‑enables auto‑reconnect after a close().
    • close(): void manually close, wait for buffered frames to flush, and stop auto‑reconnect (status → Disconnected).
    • destroy(): void teardown: remove listeners, stop timers, reject pending waitConnected/ping calls, flush buffers, close socket, status → Disconnected.

  • Status and events

    • getStatus(): ClientStatusValue returns the current status.
    • onStatusChange(cb): () => void subscribes to status changes; immediately calls cb with the current status; returns unsubscribe.

  • Latency

    • ping(timeoutMs?: number): Promise<void> sends an app‑level ping and resolves on pong or rejects on timeout.
    • getLatency(): number | undefined returns the last measured ping round‑trip time (ms).
    • onLatency(cb): () => void subscribes to latency updates; if a value exists, emits immediately; returns unsubscribe.

  • Rooms

  • join({ roomId, crdtAdaptor, auth? }): Promise<LoroWebsocketClientRoom> joins a room for a given CRDT type via its adaptor. Optional auth carries application-defined join metadata (e.g., auth/session tokens) and is forwarded to the server’s authenticate hook.

    • Room API: leave(): Promise<void>, waitForReachingServerVersion(): Promise<void>, destroy(): Promise<void>.

Status & Reconnect Model

  • Status values

    • Connecting: initial or manual connect() in progress.
    • Connected: websocket is open and usable.
    • Disconnected: socket closed. Auto‑reconnect keeps retrying unless close()/destroy() stop it.

  • Auto‑reconnect

    • Retry cadence: attempts start ~500 ms after the first unexpected close and double on each failure (1 s, 2 s, 4 s, …) up to a 15 s ceiling. A successful connection resets the backoff to the 500 ms starting point.
    • The timer is canceled when the environment reports offline; the client stays in Disconnected until an online event arrives, at which point the next retry fires immediately.
    • Calling close() or destroy() turns off auto‑retry. Invoke connect() later to restart the process with a fresh backoff window.
    • Server‑initiated kicks: if the socket closes with a code in the 4400–4499 range or a reason of permission_changed / room_closed, the client assumes the server intentionally removed the connection and does not schedule reconnect attempts. This mirrors the Durable Object kick semantics used in @loro-protocol/do.

Latency & Ping/Pong

  • Periodic pings

    • By default, the client sends a text "ping" every 20s (configurable via pingIntervalMs) and expects a "pong". This keeps the connection alive and measures round‑trip latency.
    • Set disablePing: true to turn off the timer.

  • On‑demand ping

    • Call ping(timeoutMs) to send a ping and await the next pong; rejects on timeout.
    • onLatency(cb) fires whenever a pong is observed and updates getLatency().

Rooms & Rejoin

  • Join handshake

    • join() sends a JoinRequest with the adaptor’s CRDT type, version, and optional join metadata (auth bytes).
    • On JoinResponseOk, the adaptor reconciles to the server’s version and begins streaming updates.

  • Rejoin after reconnect

    • The client tracks active rooms and their join metadata. After reconnect, it re‑sends JoinRequest for each active room and the adaptor re‑syncs.
    • If the server responds VersionUnknown, the client retries using adaptor.getAlternativeVersion() or an empty version as a fallback.
    • For %ELO, updates that arrive right after join may be buffered briefly to cover backfills that race the join.

Fragmentation & Large Updates

  • Oversize updates are split into DocUpdateFragmentHeader + DocUpdateFragment messages and reassembled on the receiver.
  • Fragmentation occurs automatically for single updates that approach the wire limit (headroom reserved under MAX_MESSAGE_SIZE). No action is required by callers.

SimpleServer (for local/e2e usage)

import { SimpleServer } from "loro-websocket/server";

const server = new SimpleServer({
  port: 8787,
  authenticate: async (_roomId, _crdt, auth) => {
    // join metadata is passed as `auth`; return "read" | "write" | null
    return new TextDecoder().decode(auth) === "readonly" ? "read" : "write";
  },
  onLoadDocument: async (_roomId, _crdt) => null,
  onSaveDocument: async (_roomId, _crdt, _data) => {},
  saveInterval: 60_000,
});
await server.start();
// Later: await server.stop(); flushes any buffered frames before terminating clients

Examples

  • Status and reconnect
const client = new LoroWebsocketClient({ url: "ws://localhost:8787" });
client.onStatusChange(s => console.log("status:", s));

// Later, stop auto‑reconnect
client.close(); // status → Disconnected

// Resume auto‑reconnect
await client.connect(); // status: Connecting → Connected
  • Latency
const off = client.onLatency(ms => console.log("latency:", ms));
await client.ping(2000);
console.log("last RTT:", client.getLatency());
off();
  • Join with join metadata/auth
const adaptor = new LoroAdaptor();
adaptor.getDoc().setPeerId(42);
await client.join({
  roomId: "project-123",
  crdtAdaptor: adaptor,
  auth: new TextEncoder().encode("write-token"), // application-defined join payload
});

Node/Web Compatibility

  • Browsers: uses the native WebSocket and window online/offline events.
  • Node: supply a WebSocket implementation (e.g. ws) via globalThis.WebSocket.
  • %ELO crypto uses Web Crypto (globalThis.crypto.subtle); Node 18+ provides it.

License

MIT